The present invention relates to lathes and analogous machine tools in general, and more particularly to improvements in means for driving the work spindle or an analogous torque receiving member of a machine tool, especially the hollow horizontal work spindle which is mounted in the headstock of a lathe and whose rear end portion extends from the headstock and carries a chuck actuating mechanism. The chuck actuating mechanism has one or more portions extending through the hollow work spindle and operatively connected with a chuck or an analogous work- or tool-holding device at the front end of the work spindle.
It is already known to transmit torque to the rear end portion of the work spindle in a machine tool by resorting to a discrete prime mover which is remote from the work spindle and to a torque transmitting unit which includes a gear removably mounted on the work spindle and a power train connecting the gear with the output shaft of the prime mover. A torque transmitting unit which can be used to drive a gear at the rear end of a work spindle is disclosed, for example, in German publication entitled "Zeitschrift fur wirtschaftliche Fertigung" (1969, Volume 2, pages 65 to 69, particularly FIG. 6). This publication discloses a separable torque transmitting unit so that, if necessary, it can be replaced with a different unit, for example, when the machine tool is to be used for a different purpose or if the decision regarding the use of a particular unit is postponed until shortly prior to final assembly or completion of the setup. A drawback of such machine tools is that the torque transmitting unit includes a wheel or gear on the exposed rear end portion of the work spindle, a gear transmission which is driven by the prime mover, as well as a belt transmission which is interposed between the gear or wheel and the gear transmission. The provision of a belt transmission necessarily limits the magnitude of torque which can be transmitted from the prime mover to the work spindle.
Another system for transmitting torque to the work spindle of a machine tool is disclosed in a German publication entitled "Werkstatt und Betrieb" (1976, Volume 2, pages 57 to 66). The gear transmission is a stationary unit which is installed next to the machine tool and transmits torque to the work spindle of the machine tool through the medium of a belt transmission. Thus, this prior construction shares the drawbacks of the construction which is described and shown in the first-mentioned German publication.